Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$180.44	5.536%	$190.4292	$190.43	$190.45	$190.40
Purchase #2	$106.92	9.705%	$117.2966	$117.30	$117.30	$117.30
Purchase #3	$45.34	11.549%	$50.5763	$50.58	$50.60	$50.60
Purchase #4	$242.32	4.226%	$252.5604	$252.56	$252.55	$252.60
Purchase #5	$141.80	9.740%	$155.6113	$155.61	$155.60	$155.60
Purchase #6	$250.67	11.865%	$280.412	$280.41	$280.40	$280.40
Purchase #7	$17.37	3.644%	$18.003	$18.00	$18.00	$18.00
7 purchase totals =	$984.86		$1,064.8888	$1,064.89	$1,064.90	$1,064.90